Chain saw safety method and apparatus

ABSTRACT

A method and apparatus for preventing injury to an operator of a chain saw of the type having a frame, a frame handle, a control handle, a guide bar, a cutting chain and power means mounted on the frame and operably connected to the cutting chain for driving the cutting chain on the guide bar. The apparatus includes a first lever pivotally mounted adjacent to the frame handle and a second lever pivotally mounted adjacent to the control handle. A self-locking brake is biased toward actuation and upon actuation is operably sufficient to instantly stop movement of the cutting chain and stall out the chain saw power means. Actuation of the self-locking brake is controlled by engaging the first and second levers against the frame and control handles respectively. This engagement is translated through a linkage system to overcome the aforementioned bias and disengage the self-locking brake. Upon release of either the first or second levers, or both, from engagement with the frame or control handles respectively the brake will be immediately actuated. The method includes the steps of controlling the actuation of a self-locking brake and actuating the brake in the event an operator&#39;&#39;s hand slips from either the frame handle or the control handle. If such an event occurs the method includes braking the cutting chain to an immediate stop and thus minimizing the possibility of injury to the operator.

United States Patent [191 Moore Feb. 26, 1974 CHAIN SAW SAFETY METHOD AND APPARATUS i [75] Inventor: Harold Edward Moore, Torrance,

Calif.

[73] Assignee: McCulloch Corporation, Los

Angeles, Calif.

[22] Filed: Oct. 4, 1972 [21] Appl. No.: 294,866

Related US. Application Data [63] Continuation-impart of Ser. No. 190,574, Oct. 19,

[52] US. Cl 30/383, 83/DIG. 1, 192/130 [51] Int. Cl B27b 17/02, B27b 17/10 [58] Field of Search 188/823, 82.4, 82.7-82.8; 192/130; 30/381, 382, 383; 83/788, 814, 815, 571, 573

[56] References Cited UNITEDSTATES PATENTS 1,189,603 7/1916 Michener .i 30/390 3,587,387 6/1971 Burrows 310/50 Mattson et al' 30/383 Moore 192/130 X Primary ExaminerDonald R. Schran Attorney, Agent, or Firm-.Burns, Doane, Swecker & Mathis ABSTRACT A method and apparatus for preventing injury to an operator of a chain saw of the type having a frame, a frame handle, a control handle, a guide bar, a cutting chain and power means mounted on the frame and operably connected to the cutting chain for driving the cutting chain on the guide bar.

The apparatus includes a first lever pivotally mounted adjacent to the frame handle and a second lever pivotally mounted adjacent to the control handle. A

self-locking brake is biased toward actuation and upon actuation is operably sufficient to instantly stop movement of the cutting chainand stall out the chain saw power means. Actuation of the self-locking brake is controlled by engaging the first and second levers against the frame and control handles respectively. This engagement is translated through a linkage system to overcome the aforementioned bias and disengage the self-locking brake. Upon release of either the first or second levers, or both, from engagement with the frame or control handles respectively the brake will be immediately actuated.

The method includes the steps of controlling the actuation of a self-locking brake and actuating the brake in the event an operators hand slips from either the frame handle or the control handle. If such an event occurs the method includes braking the cutting chain to an immediate. stop and thus minimizing the possibility of injury to the operator.

10 Claims, 8 Drawing Figures PATENTED FEB28 I974 saw u 0F 4 1 I CHAIN SAW SAFETY METHOD AND APPARATUS OTHER RELATED APPLICATIONS This application is. a continuation-in-part of applicants copending U.S. application Ser. No. 190,574 filed Oct. I9, 1971 entitled Chain Saw Safety Method and Apparatus".

BACKGROUND OF THE INVENTION Typically a chain saw is designed to be utilized by an operator grasping the machine with both hands. An operators onehand normally grips a frame handle while the other hand engages a control handle for at least actuating a trigger throttle mechanism of the type suitable for ultimately controlling the speed of the cutting chain.

' In some instances of cutting operation an operator may choose to apply downward and forward pressure on the frame handle to achieve a more rapid cutting rate. In such event, there is at least a possibility of the operators hand slipping from the frame handle toward and potentially into the rapidly moving cutting chain. In other instances of cutting operation the cutting chain may engage a limb or the like at the tip of the guide bar.

In such an event vertical movement ofthe cutting chain over the guide bar tip may induce the bar to kick upwardly in a manner commonly referred to as kick back." The abrupt action of kick back may cause an operators hand to slip from either the frame handle or even possibly the control handle and into the cutting chain. Experience indicates that if an operators hand does so accidentally slip into a rapidly moving cutting chain .the hand, and often the operators entire arm, may be badly mutilated and/or possibly severed.

At least one previously known device which may be useful for alleviating the above noted problem includes a lever arm mounted on the frame handle which when held against the handleoperates a clutch mechanism in combination with a standard chain saw clutch so that the cuttingtchain will not be operably connected to the drive shaft unless the lever on the frame handle is maintained in a depressed posture. Therefore if the operators hand should slip fromthe frame handle the clutch will be disengaged and the cutting chain will ultimately slow down and stop.

While a device, such as the above noted, may provide a degree of safety, it will readily be recognized that this known system merely serves to disengage a clutch so that momentum may carry the cutting chain at least momentarily forward. .Continued movement of the cutting chain presents a potential source of injury to an operator. Further, such a device is an integral part of the normal drive system of the chain saw and thus is in continuous use presenting wear and replacement difficulties. I

Another previously known device which constitutes a refinement over the above described system includes a clutch tripping device in combination with a band brake which is normally biased toward actuation but held from engagement by the simultaneous depression of a lever connected to'a frame handle and a lever connected to a control handle. While such a device is a notable advance over the first mentioned system, room for significant improvement remains.

,In this connection it would be highly desirable to provide a simplified system which would positively, quickly and reliably lock a cutting chain from movement in the event that an operators hand accidentally slips from a-frame handle and/or a control handle of a OBJECTS AND SUMMARY OE THE INVENTION Objects of the Invention It is therefore a general object ofthe invention to provide a novel chain saw safety method and apparatus which will obviate or minimize problems of the'type previously described.

It is a specific object of the invention to provide a novel method and apparatus to prevent injury to a chain saw operators hand in the event the operators hand accidentally slips from either a frame handle or a control handle, or both, of a chain saw toward a rapidly moving cutting chain. I

It is another object of the invention to provide a novel chain saw safety method and apparatus which is rapid in response to instantaneously lock out translation of a chain saw cutting chain in the event an operators hand slips from either a frame handle or a control handle, or both, of a" chain saw. v I

It is yet another object of the invention to provide a method and apparatus utilizing a novel articulated linkage assembly for actuating a self-locking brake means in the event an operators hand slips from a frame handle or a-control handle of a chain saw.

It is a further object of the invention to provide a method and apparatus utilizing a novel chain saw brake system which is self-locking and operatively serves to immediately stop rotation of a chain saw cutting chain upon actuation.

It is yet a further object of the invention to provide a novel chain saw safety apparatus which is highly durable, reliable and rapid in operation to effectuate stoppage of cutting motion of a chain saw cutting chain in the event an operators hand should slip from either a frame handle or a. control handle of a chain saw.

- BRIEF SUMMARY.

A preferred embodiment of the invention intended to accomplish at least s'omeof. the foregoing objects comprises a method and apparatus for preventing injury to an operator of a chain saw of the type having a frame, a frame handle, a control handle, a guide bar, a cutting chain and power means mounted on the frame and operably connected to the cutting chain for driving the cutting chain on the guide bar.

The apparatus includes a self-locking brake assembly operably connected to the cutting chain for stopping translation of the cutting chain upon the guide rail. A

brake actuation system is connected to thebrake assembly and includes a first lever pivotally mounted adjacent to the frame handle and a second lever pivotally mounted adjacent to the control handle. A first link is connected at one end to-the first lever and a second link is connected at one end to the second lever. A linkage system is connected at' one end to the other ends of the first and second links and is connected at the other end thereof to the brake assembly for maintaining the brake in an actuated posture unless the first and second levers are simultaneously held against the frame handle and the control handle respectively.

The method includes the steps of controlling actuation of a self-locking brake such that in the event an operators hand accidentally slips from the frame handle and/or the control handle a self-locking brake will be actuated for braking the cutting chain to an immediate stop. By this method the possibility of the cutting chain injuring the operators hand is minimized.

THE DRAWINGS Further objects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a pictorial view of a hand held portable chain saw wherein an operator may grasp a frame handle with one hand and a control handle with another hand for manipulation and operation of the saw and simultaneously effect actuation of the subject safety method and apparatus;

FIG. 2 is a side elevationalview, partially broken away, of a chain saw including a self-locking brake and an actuation assembly connected thereto including a first lever mounted adjacent to the chain saw frame handle and a second lever mounted adjacent to the chainsaw control handle;

FIG. 3 is a partial plan view of the chain saw including the safety system actuation assembly disclosed in FIG. 2; V

FIG. 4 is a cross-sectional view taken along section line 4-4 in FIG. 2;

FIG. 5 is a cross-sectional view taken along section line 55 in FIG. 2', and

FIGS. 6A-C are schematic views of the subject safety system in various modes of operation as follows:

FIG. 6A discloses a self-locking brake in an actuated posture in response to translation of a biased rod in the event a first lever is permitted to pivot away from engagement with the chain saw frame handle notwithstanding the fact that a second lever is in engagement withv the chain saw control'h andle;

FIG. 6B discloses a self-locking brake in an actuated posture in response to translation of a biased rod in the event a second lever mounted adjacent to the chain saw control handle is permitted to pivot away from engagement with the handle notwithstanding the fact that a first lever is in engagement with the chain saw frame handle; and 1 FIG. 6C discloses a self-locking brake in an actuated posture in response to, translation of a biased rod upon release of both a first and second lever which are mounted adjacent to a frame handle and a control handle respectively of the chain saw. I

DETAILED DESCRIPTION Referring now to the drawings wherein like numerals designate like parts and more specifically to FIG. 1 thereof, a portable chain saw 10 is shown. The chain saw 10 is of the type suitable to be held by a single operator (not shown) with one hand 12 grasping a frame handle 14 and another hand 16 grasping a control handle 18. The operators forward hand 12 is primarily used as a manipulation means to lift and apply cutting pressure to the saw while the rear hand 18 is utilized to stabilize the saw and to control the rate of travel of the cutting chain by manipulation ofa trigger throttle (not shown).

The portable chain saw 10 is designed with a body frame 20 suitable to enhouse a power means (not shown) which typically comprises a small singlecylinder two-cycle internal combustion engine. The power drive within the interior of the frame housing 20 may be operably connected to a cutting chain sprocket 22, note FIG. 4, by a centrifugal clutch assembly 23. For a more detailed illustration of typical centrifugal clutch assemblies reference may be had to any one of the U.S. Pat. Nos. 2,974,399, to Moore et al, Collins, 3,385.41 1 or Hazzard 3,425.41 1, all assigned to the assignee of the subject application.

The chain sprocket 22 drives cutting chain 24 which is supported for endless translation upon a guiderail or guide bar 26. The cutting chain serves in a conventional manner to rip or tear a kerf through a material to be severed in a well known manner of chain saw cutting operation. j 4

The portable chain saw as depicted in FIG. 1 also includes a chain saw safety system comprising an actuation assembly 28 and a cutting chain braking assembly 30. Referring now to FIGS. 2-5, there will be seen various detailed views of these chain saw safety system assemblies;

With particular reference now to FIGS. 2, 4 and 5, there will be seen variant detailed views of the selflocking braking assembly 30. More particularly a power means within the interior of the chain saw frame 20 serves to drive through a centrifugal clutching system 23 of the chain saw, as previously discussed. The exterior peripheral surface 32 of the centrifugal clutch drum 25 may synergistic-ally serve as a braking surface for the cutting chain 24 in that-the clutch drum is directly connected through sprocket 22 to the cutting chain.

In order to utilize the potential braking surface 32 of the clutch drum 25 a portion 34 of the housing 20 is extended to surround the clutch-drum. The housing portion 34 is provided with a cylindrical boss 36 which coaxially inwardly extends toward the clutch drum. The

boss 36jserves to pivotally carry a yoke 38 in a posture spaced from but contiguous to the outer faceof the clutch drum 25.

A pair of arcuately wedge-shaped brake shoes 40 are pivotally mounted at the extremities of the yoke 38 and are biased away from engagement with the brakesurface 32 by the provision of springs 42.-Also normally inwardly projecting from the frame portion 34 are a pair of frame lugs 44 which serve to surround and carry bearing rods 46 at diametrically opposed positions radially outwardly from the exterior surface 32 of the centrifugal clutch drum 25. a j

The arcuately wedge-shaped brake shoes 40 are each provided with an exterior camming surface 48 and an interior arcuate surface 50. The carnming surfaces 48 are suitable to engage the bearing rods 46 and to consequently pivot the brake shoes 40 toward the braking surface 32. The interior arcuate surfaces 50 of the brake shoes 40 serve to intimately engage the braking surface 32 in a frictional manner to stop rotation of the drum upon actuation of the brake shoes. In'this connection frictional contact between the brake shoes 40 and the braking surface 32 niay be enhanced by lining the arcuate surfaces 50 of the brake shoes with a conventional brake lining material, as desired.

In operation the clutch drum 25 is normally rotated in a clockwise direction as viewed in FIG. 2. Rotation of the yoke 38 in a clockwise direction will serve to force the camming surfaces 48 of the clutch shoes 40 into increasing engagement with the' bearing rods 46. This engagement will serve to pivot the brake shoes 40, against the bias of springs 42, until the arcuate surfaces 50 are in intimate frictional engagement with the brake surface 32. Once the shoes 40 engage the surface 32 there will be a tendency for the clutchdrum 25 to carry the shoes in a clockwise direction. Clockwise rotation of the brake shoes, however, serves to increase the wedging-camming action against the bearing rods 46 and thus merely increases the frictional-engagement between the arcuate surfaces 50 and the exterior surface 32 of the centrifugal clutch drum. Such a brake arrangement is commonly referred to as being -selflocking" and will serve .to rapidly and reliably stop rotation of the clutch drum 25 upon actuation of the brake shoes 40. i

Referring now to FIGS. 2-4, there will be seen an actuation assembly 28 suitable for use in connection with the braking assembly 30.

The actuation system 28 includes a-first lever 60 pivotally mounted adjacent to the frame handle 14 of the chain saw 10. The first lever 60 includes a transverse member 62 having an axis extending generally parallel with the axis of an upper'portion of the frame handle 14. The transverse member 62 has connected respectively to the ends thereof a first and second normally extending arm 64 and 66, note FIG. 4.

Arm 66 is provided with a normal extension 68, note FIG. 3, having an end portion 70 extending at right angles thereto for insertion within an aperture in pivot bracket 72. The pivot bracket 72 is attached to the chain saw frame 20 by the provision of conventional threaded fasteners 74, note FIG. 4. The arm 64, in a similar manner, is provided with a normally extending leg 76 which is connectedflto leg 64 by a loop 78, note FIG. 2. Thefree leg 76 is fashioned with a a normally directed segment 79 suitable to be received within an aperture in the pivot bracket 72.

By the provision of the foregoing arrangement of arms the first lever 60 is mounted for limited pivotal movement away from and toward engagement with theupper. portion of the frame handle 14. i

The actuation assembly28 further includes a second lever 80. The second lever is pivotally mounted upon the control handle 18 for movement away from and toward the handle. The lever 80 is fashioned with a generally U-shaped plate 84 designed to conform to the top surface of the control handle 18. One end of the plate 84 is bifurcated into a pair'of legs 86 for connection with a pivot pin 82 which extends through the control handle,-no'te FIG.'4.

The actuation assembly 28 further includes a longitudinally translatable rod 90, note FIG. 2, which is intimately received for translation through an aperture in a mounting frame 92 by the provision of a rubber grommet 94 or the like. One end 96 of the rod is normally bent for extension through an aperture in the yoke 38. The aperture in the yoke is radially offset from the pivot axis 97 thereof to effect pivotal movement of the yoke.

The rod is provided at approximately a mid-span portion thereof with a bearing washer 98 which is held in position by a normally extending pin 99. An abutment washer 100 is coaxially mounted upon the rod against the grommet 94 and a compression spring 102 is mounted between the washers 98 and 100 to bias the rod 90 toward the yoke to induce a clockwise rotation thereof and the brake shoes 40 into engagement with the braking surface '32 of the centrifugal clutch drum.

In order to overcome the normal bias of rod 90, which effects braking action of the cutting chain, a linkage system is provided which interconnects the first and second levers 60 and-80, respectively, with the rod 90. More specifically, a first link 1 10 is pivotally mounted at one end 111 through the loop 78 in the first lever 60. A second link 1 12 is pivotally mounted at one end 113 toan extended section 114 of the second lever 80. The other ends 116 and 118 of the first and second links and 112, respectively, are linked together at a pivotal junction by one end 120 of a third link 122. The other end 123 of the third link is looped around a hook portion 124 of the longitudinally translatable rod 90. Thus an articulated linkage assembly'is provided between the first lever 60, the second lever 80 and th longitudinally movable rod 90.

, The dimensional relationship of the first andsecond levers 60 and 80, the first and second links 110 and 112, the third link 122 and the longitudinally movable rod 90 are such that upon pivotal engagement of the first and second levers 60 and 80 into abutting engagement with the frame and control handles 14 and 18 respectively the longitudinally translatable rod 90 will be pulled against the normal bias of compression spring 102 to rotate the yoke 38 counterclockwise and draw the arcuately wedge-shaped brake shoes 40 out of engagement with the outer braking surface 32 of the cylindrical clutch drum.

OPERATION Turning now to FIGS. 6A-C, there will be seen three schematic views of the actuation and brake assemblies in various modes of operation.

Moreparticularly, and referring to FIG. 6A, in the event an operators hand should slip from the frame handle 14, the first lever '60 will pivot away from the handle.'The operators rear hand 16, however, may remain clasped about the control handle 18 and the sec,- ond lever 80 therefore is maintained in a depressed posture. a

As the first arm 60 pivots away from .the frame handle 14, as indicated by arrow A, the first link 110 is free rection D toward the brake assembly. Movement of the 7 third link 122 in turn permits the rod 90 to translate longitudinally in the direction of arrow E toward the yoke 38 under the bias of compression spring 102. The yoke 38 in turn will pivot about the central axis 97 in a clockwise direction as indicated by arrow F for an initial position shown in phantom to an actuated position shown in full lines. The arcuately wedge-shaped clutch shoes 40 will cam against the bearing rods 46 and into intimate frictional engagement with the braking surface 32 of the centrifugal clutch drum 25 to immediately stop movement of the clutch drum and the cutting chain. 7

FIG. 6B discloses an alternate possible mode of actuation. In this view the first lever 60 is engaged against the frame handle 14. The second lever 80, however, is permitted to pivot upwardly as indicated by arrow G as would be the case in the event an operator's rear hand should slip from the control handle 18. Upward movement of the second lever 80 permits the second link 112 to generally translate as indicated by directional arrow H. This translation in turn will permit the first link 110 to pivot generally in the direction of arrow I.

The combined translational motion of the second link in the general direction H and the pivotal motion of the first link as generally indicated by the directional arrow I will permit the third link 122 to generally pivot and translate downwardly as indicated by directional arrow 1. Movement of the third link in the direction of arrow .1 will in turn permit longitudinal movement of rod 90 in the direction of arrow K under the influence of the compression spring 102.

Downward movement of the rod 90 will permit the yoke 38 to pivot about the axis 97 in a clockwise direction as indicated by direction arrow L. Such clockwise movement will induce the arcuately wedge-shaped brake shoes 40 into increasing engagement with the bearing rods 46 to actuate the brake shoes into frictional engagement'with the exterior braking surface 32 of the centrifugal clutch assembly. The brake shoes will then immediately stop rotation of the clutch drum and the cutting chain.

Thus, from FIGS. 6A and 6B it will be appreciated that if an operators hand should slip from either the frame handle 14, note FIG. 6A, or the control handle 18, note FIG. 6B, the clutch drum and cutting chain will be instantly stopped by a self-locking brake so that the possibility of injury to an operators hand will be minimized. i

Whereas the cutting chain will be braked to an immediate stop if an operators hand should slip from either the control frame handle or the control handle, as illustrated and discussed in connection with FIGS. 6A and 613, if the, operators hand should simultaneously slip from both handles, the cutting chain will also immediately be stopped. The possibility of this occurrence is illustrated in FIG. 6C.

In the event that an operators band should slip from the frame handle 14, the first lever 60 will be permitted to pivot in a general direction as indicated by arrow M. If the operators other hand should slip from'the control hand 18, the second lever 80 will be permitted to rotate upwardly as generally indicated by arrow N.

Rotational movement of the first and second levers 60 and 80, respectively, in the general direction of arrows M and N, will permit'the first and second links 110 and 112m move generally in the direction of arrows 0 and P respectively. Such movement of the first and second links permits the third link 122 to move in the general direction of arrow Q. In turn, the longitudinally movable rod is permitted to move in the direction of arrow R under the influence of compression spring 102 to pivot the yoke 38 about the axis 97 in a clockwise direction as indicated by directional arrow S.

The arcuately wedge-shaped brake shoes 40 will pivot against bearing rods 46 to bring friction surface 50 of the brake shoes 40 into engagement with braking surface 32. The clutch and thus the cutting chain will thereupon be instantly frozen against rotation, as previously discussed, by the self-locking brake assembly.

SUMMARY OF THE MAJOR ADVANTAGES It will be appreciated by those skilled in the art that the above described invention discloses a method and apparatus for minimizing disastrous accidents of the type which may occur when an operators hand accidentally slips from a chain saw frame handle or control handle into the cutting chain.

The cutting chain is braked to an immediate stop by a novel self-locking brake assembly which I may be symergistically associated with a conventional contrifugal clutch drum.

A highly significant aspect of the subject invention is the provision of levers adjacent to both the frame and control handles of the chain saw for actuating the selflocking brake upon the operators hand slipping from either the frame or control handle to instantly actuate the brake. Theactuation assembly includes a unique linkage arrangement which is rugged, reliable and rapid acting to permit a self-locking brake which is normally biased into engagement to rapidly lock upon slippage of an operators hand from either the frame or the control handle.

Still further, the subject chain saw safety system is maintained in a disengaged postu're under normal operations and therefore it'does not continuously coact with the cutting chain drive train which potentially may create servicing and wear difficulties.

Although the invention is disclosed with reference to a preferred embodiment it will be appreciated by those skilled in the art that additions, deletions, modifications, substitutions and other changes not specifically described and illustrated in this embodiment may be made which will fall within the purview of the appended claims.

What is claimed is: s

1. A chain saw adapted to be held by an operator using both hands comprising:

a frame having, I.

a frame handle, and a control handle; A

a guide rail connected to said frame;

a cutting chain operably carried by said guide rail;

power means mounted on said frame and operably connected to said cutting chain for driving said cutting chain on said guide rail;

brake means operably connected to 'said cutting chain for stopping movement of said cutting chain on said guide rail; and

brake actuation means connected to said brake means for controlling the application of said brake means including,

a first lever pivotally mounted adjacent to said frame handle,

a second lever pivotally mounted adjacent to said control handle,

a first link connected at one end to said first lever,

a second link connected at one end to said second lever,

linkage means connected at one end to the other ends of said first and second links and connected at the other end to said brake means for maintaining said brake means in an actuated posture unless the first and second levers are held against the frame handle and the control handle, respectively.

2. A chain saw as defined in claim 1 wherein said linkage means comprises:

a rod mounted for longitudinal translation toward and away from said brake means and connected at one end thereof to said brake means;

means for normally biasing said rod toward said brake means to maintain said brake means in an actuated posture; and

a third link pivotally connected at one end thereof to the other end of said rod and pivotally connected at the other end thereof to the other ends of said first and second links.

3. A chain saw as defined in claim 2 wherein said means for biasing comprises:

a compression spring coaxially surrounding said rod and abutted against a frame stop at one end thereof and connected to a generally midspan portion of said rod at the other end thereof.

4. A chain saw as defined in claim I wherein said brake means comprises:

a self-locking brake.

5. A chain saw as defined in claim 1 wherein said brake means comprises:

a generally cylindrical brake drum operably connected to said cutting chain;

at least one arcuately wedged-shaped brake shoe operably carried adjacent the periphery of said drum and normally biased away from engagement therewith; and

at least onestationary frame lug fixedly connected to said frame and positioned adjacent said at least one brake shoe.

6. A chain saw as defined in claim 5 wherein:

said at least one arcuately wedge-shaped brake shoe comprises a pair of diametrically spaced brake shoes, pivotally supported upon a yoke connected therebetween; and

said at least one stationary frame comprises a pair of frame lugs each one positioned on said frame adjacent a corresponding one of said pair of brake shoes.

7. A chain saw as defined in claim 6 wherein:

said other end of said linkage means is connected to the yoke of said brake means for pivoting said yoke and actuating said spaced brake shoes into and out of wedging engagement between said frame lugs and said brake drum.

' 8. A chain saw safety device operable to be attached I 10 to a chain saw of the type having a frame, a frame handle, a control -handle,.a guide rail, a cutting chain and power means mounted on the frame and operably connected to the cutting chain for driving the cutting chain upon the guide rail wherein the improvement comprises:

brake means operably connected to said cutting chain for stopping movement of said cutting chain upon said guide rail; and brake actuation means connected to said brake means for controlling the application of said brake means including, a first lever pivotally mounted adjacent to said frame handle, a second lever pivotally mounted adjacent to said control handle; a first link connected at one end to said first lever,

a second link connected at one end to said second lever; and

linkage means connected at one end to the other ends of said first and second links and connected at the other end to said brake means for maintaining said brake means in an actuated posture unless both of said first and second levers are held against the frame handle and the control handle respec tively.

9. A chain saw as defined in claim 8 wherein said linkage means comprises:

a rod mounted for longitudinal translation toward and away from said brake means and connected at one end thereof to said brake means;

means for normally biasing said rod toward said brake means to maintain said brake means in an actuated posture; and

a third link pivotally connected at one end thereof to the other end of'said rod and pivotally connected at the other end thereof to the other ends of said first and second links.

10. A chain saw safety device as defined in claim 9 wherein said brake means comprises:

a generally cylindrical brake drum operably connected to the cutting chain;

at least one arcuately wedge-shaped brake shoe operably positioned adjacent to but normally spaced from the outer periphery of said drum;

at least one stationary frame lug fixedly connected with the frame and positioned adjacent said at least one brake shoe to serve as an abutment when said shoe is actuated against said drum; and

a yoke pivotally mounted upon the frame and lying adjacent to said brake drum, said yoke being operable to carry said at least one arcuately wedgeshaped brake shoe and being connected to said longitudinally translatable rod, whereby actuation of said longitudinally translatable rod pivots said yoke for actuating said at least one arcuately wedgeshaped brake shoe between said at least one stationary frame lug and the outer periphery of said generally cylindrical brake drum to immediately stop rotation of said drum and movement of the cutting chain. 

1. A chain saw adapted to be held by an operator using both hands comprising: a frame having, a frame handle, and a control handle; a guide rail connected to said frame; a cutting chain operably carriEd by said guide rail; power means mounted on said frame and operably connected to said cutting chain for driving said cutting chain on said guide rail; brake means operably connected to said cutting chain for stopping movement of said cutting chain on said guide rail; and brake actuation means connected to said brake means for controlling the application of said brake means including, a first lever pivotally mounted adjacent to said frame handle, a second lever pivotally mounted adjacent to said control handle, a first link connected at one end to said first lever, a second link connected at one end to said second lever, linkage means connected at one end to the other ends of said first and second links and connected at the other end to said brake means for maintaining said brake means in an actuated posture unless the first and second levers are held against the frame handle and the control handle, respectively.
 2. A chain saw as defined in claim 1 wherein said linkage means comprises: a rod mounted for longitudinal translation toward and away from said brake means and connected at one end thereof to said brake means; means for normally biasing said rod toward said brake means to maintain said brake means in an actuated posture; and a third link pivotally connected at one end thereof to the other end of said rod and pivotally connected at the other end thereof to the other ends of said first and second links.
 3. A chain saw as defined in claim 2 wherein said means for biasing comprises: a compression spring coaxially surrounding said rod and abutted against a frame stop at one end thereof and connected to a generally midspan portion of said rod at the other end thereof.
 4. A chain saw as defined in claim 1 wherein said brake means comprises: a self-locking brake.
 5. A chain saw as defined in claim 1 wherein said brake means comprises: a generally cylindrical brake drum operably connected to said cutting chain; at least one arcuately wedged-shaped brake shoe operably carried adjacent the periphery of said drum and normally biased away from engagement therewith; and at least one stationary frame lug fixedly connected to said frame and positioned adjacent said at least one brake shoe.
 6. A chain saw as defined in claim 5 wherein: said at least one arcuately wedge-shaped brake shoe comprises a pair of diametrically spaced brake shoes, pivotally supported upon a yoke connected therebetween; and said at least one stationary frame comprises a pair of frame lugs each one positioned on said frame adjacent a corresponding one of said pair of brake shoes.
 7. A chain saw as defined in claim 6 wherein: said other end of said linkage means is connected to the yoke of said brake means for pivoting said yoke and actuating said spaced brake shoes into and out of wedging engagement between said frame lugs and said brake drum.
 8. A chain saw safety device operable to be attached to a chain saw of the type having a frame, a frame handle, a control handle, a guide rail, a cutting chain and power means mounted on the frame and operably connected to the cutting chain for driving the cutting chain upon the guide rail wherein the improvement comprises: brake means operably connected to said cutting chain for stopping movement of said cutting chain upon said guide rail; and brake actuation means connected to said brake means for controlling the application of said brake means including, a first lever pivotally mounted adjacent to said frame handle, a second lever pivotally mounted adjacent to said control handle; a first link connected at one end to said first lever, a second link connected at one end to said second lever; and linkage means connected at one end to the other ends of said first and second links and connected at the other end to said brake means for maintaining said brake means in an actuated posture unless both of said first and secoNd levers are held against the frame handle and the control handle respectively.
 9. A chain saw as defined in claim 8 wherein said linkage means comprises: a rod mounted for longitudinal translation toward and away from said brake means and connected at one end thereof to said brake means; means for normally biasing said rod toward said brake means to maintain said brake means in an actuated posture; and a third link pivotally connected at one end thereof to the other end of said rod and pivotally connected at the other end thereof to the other ends of said first and second links.
 10. A chain saw safety device as defined in claim 9 wherein said brake means comprises: a generally cylindrical brake drum operably connected to the cutting chain; at least one arcuately wedge-shaped brake shoe operably positioned adjacent to but normally spaced from the outer periphery of said drum; at least one stationary frame lug fixedly connected with the frame and positioned adjacent said at least one brake shoe to serve as an abutment when said shoe is actuated against said drum; and a yoke pivotally mounted upon the frame and lying adjacent to said brake drum, said yoke being operable to carry said at least one arcuately wedge-shaped brake shoe and being connected to said longitudinally translatable rod, whereby actuation of said longitudinally translatable rod pivots said yoke for actuating said at least one arcuately wedge-shaped brake shoe between said at least one stationary frame lug and the outer periphery of said generally cylindrical brake drum to immediately stop rotation of said drum and movement of the cutting chain. 